The spectrin membrane skeleton is a ubiquitous, submembranous cytoskeleton that associates with the cytoplasmic surface of membranes. Genetic defects and deficiencies in erythrocyte isoforms of membrane skeleton components give rise to hemolytic disorders in humans. Two functions have been identified for the spectrin membrane skeleton: the maintenance of plasma membrane structural integrity and the formation of discrete membrane domains enriched in classes of membrane proteins. The recent identification of Golgi localized isoforms of membrane skeleton proteins reveals an even broader potential role for the membrane skeleton in the regulation of cellular architecture. The goal of this proposal is to characterize this Golgi membrane skeleton and to determine its function. It is hypothesized that the Golgi isoform of the membrane skeleton serves two critical functions which are analogous to the functions proposed for the plasma membrane isoforms: the maintenance of Golgi membrane structural identify and the formation of distinct membranes involved in membrane protein sorting within the Golgi complex. The specific questions that will be addressed are: 1. Are Golgi membrane skeleton proteins unique isoforms specialized for Golgi function? The precise identify of Golgi membrane skeleton proteins spectrin and ankyrin will be identified by molecular cloning. These studies will be essential for subsequent aims. 2. Will the identification of membrane skeleton bind proteins reveal critical features of the structure and function of the Golgi membrane skeleton? It is proposed that cytoplasmic binding proteins will be regulators of membrane skeleton assembly and integral membrane proteins that interact with the membrane skeleton assembly and integral membrane proteins that interact with the membrane skeleton will be "substrate proteins" acted on my membrane skeleton. The identification of these proteins will therefore provide important information regarding the assembly of the membrane skeleton as well as its protein. 3. Will dominant negative perturbations of the Golgi membrane skeleton illustrate a role for the Golgi membrane skeleton in the maintenance of Golgi structure and the formation of distinct membrane domains? Dominant negative disruption of the Golgi membrane skeleton will be performed in intact cells to directly test the proposed functions of the novel cytoskeletal structure.